Lecture 3 Membrane Potentials and Action Potentials Flashcards
Cell Body
Houses the nucleus and other typical cell organelles
The plasma membrane around the cell body is characterized by local potentials
Voltage gated ion channels are NOT characteristic of the cell body membrane
Dendrites
Cellular extensions of the neuron
The number is typically a few to many
Dendrites are characterized by the presence of ligand (neurotransmitter) -gated channels
Conduct local potentials
This houses the nucleus and other typical cell organelles
The cell body
Dendrites conduct
Local potentials
Axon
A neuron characterized by a single axon that is variable in length
An extension of the cell body and is typically opposite the side of the cell body where the dendrites are located
An extension of the cell and is covered by the plasma membrane (axolemma)
Axolemma
Characterized by the presence of voltage-gated ion channels and the ability to conduct an action potential
Distal end of axon
Characterized by the presence of membrane-bound vesicles filled with neurotransmitters
Neuron is characterized by
a single axon this is variable in length
Myelinated axon looks like
sausage because it is myelinated
Telodendria
Means end branches
Cell membrane aka
Plasmalemma
Cell membrane functions to
maintain separate intracellular and extracellular environments
Ion concentrations between intracellular and extracellular environments
Can change depending on whether or not the plasmalemma is permeable to specific ions at given periods of time
These ions are more highly concentrated outside the cell
Sodium and chloride
Ion more concentrated inside of cell
Potassium
Diffusion Potential
A diffusion potential is caused by an ion concentration difference on the two sides of a membrane.
*transitory
Nernst Potential
The diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane
Nernst Equation
E = +- 61 x log [Co]/[Ci]
Nernst Equation is used to determine
The diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane. It measures the potential for one ion at a time
Nernst Equation measures
The potential for one ion at a time
To measure the combined potential for more than one ion
The Goldman equation may be used
E =
The difference in the electrical potential between inside and outside the neuron
Nernst potential
Principal of electrical neutrality
At equilibrium the concentration of ions should be the same
Resting membrane potential of nerves
Sodium-Potassium pump
Characteristics of action potential
All or none, will occur or won’t
Self-propagating, each region of depolarization serves to generate action potentials on either side
Non-decremental, does not decrease in strength
Action potential is all or none
It will either occur or not
Action potential is self-propagating
each region of depolarization serves to generate action potentials on either side
Action potential is non-decremental
It does not decrease in strength
Ion channels
Are channels that allow the passage of ions from one side of the membrane to the other
Typically very selective, allowing only one kind of ion to pass through
How selective are ion channels?
Very selective, one kind of ion is allowed to pass through
Ion channels are open
When certain conditions are met
Slow-leak channels are
always open
Two types of gated ion channels are
Ligand gated
Voltage gated
Voltage gated sodium channels have two gates
Activation Gate
Inactivation Gate
Activation gate is closed at
-90mV
The resting potential
-90mV
The activation gate is closed and the inactivation gate is opened
With the inside of the axon membrane negative relative to the outside
Activation gate open, inactivation gate closed
+35mV - -90mV
Potassium-gated channels
Have a single gate
Gate is closed at a resting potential of -90mV
Slow activation opens the gate from +35 mV to -90mV
Action Potential Propagation
Steps in the generation of an action potential on a neuron axon membrane
- Resting Stage
- Depolarization Stage
- Repolarization Stage
- Sodium and potassium conductance
Resting Stage
1st step in the generation of an action potential
-90mV
Depolarization Stage
Membrane suddenly becomes permeable to sodium ions
Membrane potential may overshoot for large axons
Repolarization Stage
Sodium channels close within a few 10,000ths of a second
Potassium channels open more than normal
Action Potentials
Current flowing down the inside of an axon at a particular point can continue down the interior of the fiber or cross the membrane at that point.
Threshold
Point at which a local potential will elicit an action potential
-65mV (highly variable)
Action Potential Direction of Propagation
Action potential travels in all directions form the point of stimulation
- Orthodromic direction
- Antidromic direction
Orthodromic Direction
Of an action potential
Direction normally taken
Antidromic Direction
Of an action potential
Opposite direction than normally taken
As K+ goes out…
Gets more negative because losing +
Myelination - 3 parts
- Sphingomyelin
- Schwann cell
- Node of Ranvier
Sphingomelin
(myelination)
Lipid, laid down by Schwann cells
Schwann cell
(myelination)
Wraps around axons in peripheral nervous system
Node of Ranvier
(myelination)
Gaps between Schwann cells, has to jump from one Node of Ranvier, called Saltory conduction
Saltatory Conduction
Jumps from one node to the next
- Increases velocity of nerve transmission
- Allows 100x less loss of ions and requires little energy for repolarization
Fiber diameter
If you increase diameter, can increase surface area, resistance decreases
Characteristics of axon that carries signal the fastest
Myelinated axon
Large diameter
Ex. Skeletal muscle movement
Characteristics of axon that carries signal the slowest
Nonmyelinated
Small diameter
Ex. Pain signals
Function of a Schwann cell
to insulate nerve cells
Where waves of depolarization occur
Node of Ranvier
Absolute refractory period
Right after the action potential
Period during which a second action potential cannot be elicited even with a strong stimulus
Relative refractory period
Stronger than normal stimulus can cause action potential
-usually in lab setting
Changing ion concentrations
Describe how changes in environmental ion concentrations alter membrane potentials
